Hoop locks sometimes include a shackle including a pair of feet, a crossbar operable to receive the feet, and a locking mechanism which selectively prevents removal of one of the feet from the crossbar. In some hoop locks, one of the feet is angled, and the locking mechanism engages the straight foot. When the locking mechanism is unlocked, the shackle can be pivoted about the bent foot to remove the straight foot from the crossbar. Some such systems have certain limitations such as, for example, those relating to resistance to tampering or attack. Therefore, a need remains for further improvements in this technological field.